Three-fluid heat exchanger



United States Patent 721 Inventors Irvin: Almlll 2,566,310 9/1951 Burns6H1] 165/140 Inglewood; 2,617,634 11/1952 Jendl'aSSlle 165/140 i DavidG-Brldgnelbkolhng Hills, and 2,634,958 4/1953 Simpelaar 165/166 1 9 9 C-KiIIBeILLDS Angeles, California 2,658,728 11/1953 Evans l65/i 21 1 Appl.No. 11. 2,793,836 5/1957 Holmes 165/165x 21 Filed March 11,19682,846,198 8/1958 Sturges l65/166X 451 Patented Nov- 3. 19 0 2,948,5168/1960 Martinelli.. 1 65/1 3] Assielwe The 6mm Cowl-9119a 3,451,4736/1969 Urie :61. 165/70x L08 Angeles, l i m l 3,469,623 9/1969 Rawlings165/166X 8 coml'lufln of California 619,325 5/1961 Canada 165/166804,592 11/1958 Great Britain 165/70 [541 32:2 3 E EXCMNGER 819,8259/1959 Great Britain 165/70 B 922,632 4/1963 Great Britain 165/70 52 US.Cl 165/70, 1,499,286 9/1967 France 165/70 I CI 165,140 165,134 PrimaryExaminer-AlbertW. Davis, Jr. [51] nt. Hus/06 AmmefWJohn N. Hazelwwd.Albert Miller and Orville 50 Field ofSearch 165/70, same ABSTRACT: Aheat exchanger utilizing a pressurized buffer [5 6] References Citedfluid between the coolant and the fluid to be cooled, to reduce UNITEDSTATES PATENTS thermal stress, and to prevent the intermixing of thecoolant 1,182,550 5/1916 Freeman 165/104 with the fluid to be cooled.

Patented Nov. 3, 1970 Sheet 1 of 4 INVENTORS. IRVING G. AUSTIN DAVIDG.BRIDGNELL BY ROBERT C.K|N$ELL ATTORNEY Patented Nov. 3, 1970 Z of 4Sheet Patented Nov. 3, 1970 3,537,513

Sheet 3 0f 4 Patented Nov. 3, 1970 3,537,513

Sheet 4 0:4

OOOOOOOOOOOODOOOOOOOOO THREE-FLUID HEAT EXCHANGER Up to now, heatexchangers are generally of the plate type comprising an assembly offlat platelike elements which are situated in spaced parallelrelationship. Adjacent plate elements are separated at two oppositeedges by spacer elements to define a plurality of crisscrosspassageways. Each passageway consists of two rectangular plate elementswith two spacer elements disposed at opposite edges. Alternatepassageways communicate with a first manifold and the remainingpassageways communicate with a second manifold. The coolant fluid isfed'into the first manifold and the fluid to be cooled is fed into thesecond manifold. Then obviously the two fluids would be disposed onopposite sides of the plate elements, and if any defects or leaks appearin the heat exchanger the two fluids would mix. Mixing of the fluids isundesirable and dangerous, especially if one fluid is hot engine bleedor ram air, which is to be cooled with liquid fuel, as could beencountered in the ventilation systems on supersonic aircrafts. Inaddition, if the heat exchangers of the prior art should break down,fuel leaking into the hot air passages would ignite making an infernoout of the passenger cabin.

Therefore, an object of this invention is to provide a fluid chamberbetween the coolant fluid of the heat exchanger and the fluid to becooled, which fluid chamber is preferably pressurized above the level ofthe others.

Another object of this invention is to provide a buffer fluid in a heatexchanger to reduce severity of structural temperature gradients andthermal stresses which, in turn, prevent leakage.

Another object is to prevent flash heating of the fuel, which is alsothe coolant, during momentary stoppage of the fuel flow.

Another object of this invention is to prevent leakage and intermixingof the coolant and the fluid to be cooled.

Another objective is to prevent any external surface of the heatexchanger, including the hot air inlet duct, from reaching potentialfuel ignition temperature.

Briefly, the invention provides parallel-spaced, plate elements shaped,for example, rectangular. Within alternate spaces between the plateelements are disposed hollow tubular members or headers preferably alongthelonger edges to form passageways for the hot fluid. In addition,within the remaining alternate spaces are disposed hollow headers alongthe shorter edges so that all plate elements are fastened together in astack. Therefore, between the hot fluid passageways additionalpassageways are formed which communicate with manifolds disposed onopposite ends forming a closed vessel for the buffer fluid. A flatcompartment is disposed within each passageway that communicates betweenthe manifolds. The flat compartments are spaced from the plate elementsand headers so that the buffer fluid completely surrounds the flatcompartments. Each flat compartment has an inlet means and an outletmeans so the coolant fluid passes through the flat compartment. In orderto reduce thermal stresses to a minimum, suitable holes areformed in thehollow headers so that the buffer fluids flow freely in and out of theheaders.

The foregoing and other objects, advantages and characterizing featuresof this invention will become apparent from the ensuing detaileddescription of the illustrative embodiment thereof, reference being madeto the accompanying drawings wherein:

FIG. 1 is a pictorial view of a portion of the novel exchanger withportions broken sway;

FIG. 2 is a small scale side elevation of the heat exchanger shown inFIG. 1;

FIG. 3 is a section of a portion of the heat exchanger taken on line 33in FIG. 2;,

FIG. 4 is a section of a portion of the heat exchanger taken on line 4-4on FIG. 2;

FIG. 5 is a partial elevation showing the air inlet of the heatexchanger with portions broken away to show the internal structure; and

FIG. 6 is the side elevation of the heat exchanger with the side plateremoved and portions broken away to show the internal structure.

Referring to the drawings and to FIG. I in particular, a pictorial viewof a portion of the novel heat exchanger is shown,

portions of the unit being broken away to show its structure.

The heat exchanger has a rectangular inlet flange 11 for the fluid to becooled, for example, hot bleed air from a jet engine of a supersonicaircraft, and has a rectangular outlet flange 12 that forms the outletfor the cooled bleed air. Suitable ducting (not shown) could be boltedto flanges 11 and 12 to feed the hot air into and to guide the cooledair from the exchanger, respectively. Also a compartment flrewall (notshown) could be placed between the inlet duct and flange 11 for reasonsthat will be hereinafter explained. The air leaving the exchanger hasbeen cooled, for example, by relatively cold fuel, entering theexchanger through a fuel inlet 13 and leaving through a fuel outlet 14.The fuel inlet and outlet extend through a side plate l6 that extendsfrom and is brazed to flange l1 and to flange 12. A similar side plate17 (FIG. 5) is disposed on the other side of the exchanger and parallelto the side plate 16. A semicylindrical plate 18 (FIG. 1) is disposed onthe top of the exchanger and suitably welded to side plates 16 and 17and flanges 32d on members 32, disposed at the inlet and outlet, to forma buffer fluid manifold at the top thereof. Another semicylindricalplate 19 (FIG. 6) is disposed on the bottom of the exchanger and weldedto side plates 16 and 17 and flanges 33d (FIG. 6) on members 33 (alsodisposed at the inlet and outlet) to form a buffer fluid manifold at thebottom thereof. There is disposed between the side plates 16 and 17 aplurality of heat transfer plates 21 in parallel relationship and spacedapart from each other. Plates 21 are preferably rectangular, and withinalternate spaces formed therebctween and along both vertical edges aredisposed vertical hollow headers or spacers 22 to form passagewaysextending vertically as viewed in FIG. 1. Top horizontal hollow headersor spacers 23 and bottom hollow horizontal headers or spacers 24 (FIG.5) are disposed in the other interplate spaces along the top and thebottom edges, respectively, of plates 21 to form passageways extendingright to left as viewed in FIG. 1. Horizontal and vertical passagewaysare thus formed between the plates 21. For reasons that will beexplained hereinafter, vertical hollow headers or spacers 22a aredisposed between the side plate 16 and the adjacent heat transfer plate21 and between the side plate 17 and its adjacent heat transfer plate 21to form vertical passageways. Both vertical and horizontal spacers 22,22a, 23 and 24 are rectangularly shaped tubes, to allow a buffer fluidto flow therethrough. Top and bottom spacers 23 and 24 have their endssealed with suitable plugs 25 (FIGS. 1 and 5), and therefore to allowbuffer fluid to flow therein, holes 27 are formed only on the topsurface of top spacers 23 and only on the bottom surface of bottomspacer 24 (FIG. 3).

The hot bleed air enters the heat exchanger through flange l1, and thevertical headers 22 and 22a limit the passage of air to alternatehorizontal passageways formed between the plates 21. To increase theheat transfer rate suitable offset corrugations 31 FIG. I are placedbetween the respective plates 21 in the bleed air passages. Stiffenermembers 32 and 33 are preferably extruded sections having three flangessuch as flanges 32b, 32c and 32d as shown on member 32. As mentionedabove, flanges 32 don both the inlet and outlet are butt-welded to topplate 18 as shown in FIG. 6; flanges 32c extend downward over theplugged end of headers 23 and are brazed thereto; and flanges 32b arewelded to flanges 11 and 12 of the heat exchanger. The sharp corner iseliminated between flanges 32b and 32c by suitable fillet radius. Therespective flanges on members 33 are butt-welded to bottom plate 19,brazed to the bottom plugged end of the spacers 24, and welded to theflanges I1 and 12. Each member 32 and 33 has aligned spaced lugs 37(more clearly shown in FIG. 6) disposed parallel to flanges 32c and 33c.The lugs 37 are disposed behind vertical headers 22 so that the headersare held firmly between and brazed to the lugs 37 and flange 32c and33c, respectively. The vertical bars forming flange 11 are welded to therespective side plates 16 and 17 (FIG. 5). For reasons that will beexplained hereinafter horizontal arcuated plates 38 (FIG. 6) are weldedto the outside edge of the horizontal bars of flange 11 and to therespective top and bottom plates 18 and 19, while vertical arcuatedplates 39 (of which only one plate is shown in FIG. 1) are welded to theoutside edges of vertical bars of flange 11 and to respective sideplates 16 and 17.

Since the bleed air passes only through the horizontal passagewaysformed between alternate adjacent pairs of plates 21 and runningsubstantially from flange 1 1 to flange 12, a feature of this inventionis to provide a buffer fluid on the opposite side of the plates 21 incontact with the bleed air. The buffer fluid is disposed within thevertical passageways communicating with a top manifold formed by the topplate 18 and with a bottom manifold formed by the bottom plate 19. Apressure relief valve 41 (FIG. 2) is suitably connected to the topmanifold 18 to prevent excessive pressure from building up if, forexample, the fuel (coolant) is shut off, the bleed air would cause someof the buffer fluid to heat up, causing the pressure thereof to rise.Preferably the buffer fluid is a liquid so that a thermal inertia isbuilt into the heat exchanger to prevent excessive thermal gradients.The heat is removed from the bleed air by the cold fuel entering thefuel inlet 13 and leaving outlet 14. The structure, that allows the fuelto extract heat from the buffer fluid and in turn the bleed air, willnow be explained. The inlet 13 is made substantially the same as theoutlet 14 and they include pipes 44a and 44b (FIG. 1) respectively, towhich are fixed flanges 46a and 46b. Both pipes 44a and 44b pass throughthe side plate 16 and enter the bottom buffer fluid manifold, moreclearly shown in FIG. 5. The pipes then pass through a plurality ofplates or walls 47a and 47b. Plates 47a and 47b are suitably brazed topipes 44a and 44b. Plates 47a and 47b are contoured plates having thesame configuration, and are placed face to face as shown in FIG. 4 sothat the vertical edges 48a and 48b and the top and bottom edges 48c and48d (FIG. 6) respectively, on the two plates coincide face to face andare brazed together. Each plate has a center rib 49 that extends fromthe bottom edge 48d and touches the center rib on its mating plate sothat when the two ribs are brazed together, a flat U-shaped chamber isformed between the two plates 47a and 47b (more clearly shown in FIG.6). In the portion of the pipes 44a and 44b located in the chamberformed by the plates 47a and 47b, suitable openings 51 are formed asshown in FIG. 3 for pipe 440. These openings 51 allow the cooling fluidto leave pipe' 44a, pass through the plurality of U-shaped chambers,enter pipe 44b to leave the heat exchanger. Within the U-shaped chambersare disposed suitable offset corrugations 52 disposed so that heat isefficiently transferred from the plates 47a and 47b to the coolingfluid.

In addition to the corrugations 52 disposed between two adjacent plates47a and 47b similar offset corrugations 53 (FIG. 1) are disposed totransfer heat between plates 21 and the adjacent respective plates 47aand 47b. The offset corrugations 53 are oriented to allow the bufferfluid to move freely in the vertical direction. In addition toincreasing the flow of heat, the offset corrugations 53 providestructural support for the plates 47a and 47b. Tubes 55 are disposedvertically and along both vertical edges 48a and 48b of plates 47a and47b as shown in FIG. 4 to prevent the edges from distorting underpressure due to lack of support beyond the corrugations 53. The tubes 55are opened at the top and bottom thereof so that the buffer fluid flowsfreely through the tubes. As mentioned before, offset corrugations 31are disposed between two adjacent plates 21. Corrugations 31 aredisposed to allow the air to move freely through the horizontalpassageway and efficiently transfer its heat to the coolant fuel in thefollowing sequence: hot air to corrugations 31, corrugation to plates21, to corrugations 53, to plates 47, to corrugations 52 and to coldfuel.

When exchangers use highly flammable fuels as the heat sink medium,safety features are required. In normal operation, the flange 11 wouldbe bolted against a firewall (not shown) so that the flammable fluidsare disposed on the heat exchanger side and high temperature elementsare disposed come in contact with the exterior surfaces of the heatexchanger which are maintained at a relatively low temperature by thebuffer fluid. In addition, since holes 26, 34a and 34b allow the bufferfluid to flow within curve plates 38 and 39, these plates are alsomaintained at relatively low temperature by the buffer fluid. Therefore,at substantially any place, one would choose, on the exposed surface ofthe heat exchanger, except the outlet end which is always cool, the

buffer fluid would be disposed on the opposite side. Since flange 11 isrelatively wide any heat flowing outward through the flange would beextracted by the buffer fluid contained within the curved plates 38 and39.

In addition, since the air flowing through the heat exchanger would besupplied to the aircraft cabin, no fuel and air must mix for health andsafety reasons. Since there could be a possibility of a leak in the heatexchanger, the leak would most likely occur either between the fuel andthe buffer fluid or between the air and the buffer fluid. Therefore thebuffer fluid keeps the air and fuel apart. If by the remote chance twoleaks occur, one between the buffer fluid and the fuel and the otherbetween the buffer fluid and the air, the fuel and air are preventedfrom mixing since the compartment containing the buffer fluid ispressurized, for example, by the buffer fluid accumulator 60 and therelief valve 41 to a pressure greater than both the fuel and the air.This causes the buffer fluid to flow outward and prevents the fuel andair from flowing inward into the buffer compartment. Therefore, by theuse of a buffer fluid accumulator 60 the pressure and volume can bemonitored and a loss in buffer fluids indicates a malfunction. Inaddition, if there is a short period of no fuel flow to draw away theheat, the device automatically makes use of the heat of vaporization ofthe buffer fluid to cool the air before it enters the passenger cabin.This feature should allow sufficient time to shutoff the associatedair-conditioning system before the cabin temperature rises to dangerouslevels. The bufferfluid would preferably be water to obtain the bestheat transfer properties. It may be necessary to add a freezesuppressant, such as glycol, in order to operate at low ambienttemperature. An inert type gas, such as nitrogen, can also be consideredas a buffer fluid in the event that it is not to be utilized as asecondary heat sink. y

In the light of the above teachings, various modifications andvariations of the present invention are contemplated and will beapparent to those skilled in the art without departing from the spiritand scope of the invention. Therefore, the invention is not limited tothe exemplary apparatus or precedures described, but includes allembodiments within the scope of the claims.

We claim:

1. A heat exchanger comprising:

an enclosure for containing a buffer fluid;

a plurality of spaced parallel plates disposed within said enclosure;

a plurality of first spacer elements arranged between alternately spacedparallel plates to define a plurality of first ducts for the passage ofa first fluid;

a plurality of second spacer elements arranged between the alternatelyspaced parallel plates not including said first spacer elements todefine a plurality of second ducts, each of said second ducts openinginto the enclosure and being disposed in relation to the enclosure toallow the flow of the buffer fluid therebetween; said first and saidsecond spacer elements are tubular and provided with apertures for thebuffer fluid to communicate with the interior thereof;

a plurality of third ducts for the passage of a second fluid, said thirdducts disposed within said plurality of second ducts;

heat transfer elements disposed within said second ducts in a heattransfer relationship between said third ducts and the plates of saidsecond ducts; and

manifold means disposed within said buffer fluid enclosure and operablyconnected to said plurality of third ducts to deliver and discharge thesecond fluid therefrom.

2. The heat exchanger of claim 1 wherein:

each of said third ducts comprises at least two plate walls disposedwithin each of said second ducts, said plate walls contoured to have thesame configuration and disposed face-to-face with their contactingportions bonded together; I

said manifold means disposed within said buffer fluid enclosure includesat least one pipe extending through each of said third ducts, said, pipehaving openings in the portions passing through said third ducts;

a reinforcement element disposed between at least one bonded portion ofsaid contoured plate walls and the adjacent plate of said second duct toposition said third ducts within said second ducts;

first corrugated elements disposed between said two plate walls of saidthird ducts;

said heat transfer elements comprise second corrugated elements disposedbetween said third ducts and said spaced parallel plates of said secondducts; and

third corrugated elements disposed within said first ducts.

3. The heat exchanger of claim 2 wherein:

stiffening elements are disposed on opposite sides of the inlets of saidfirst ducts and are bonded to said buffer fluid enclosure;

each stiffening element has a first flange extending outwardly form theinlet of said first ducts and the two exterior plates have portionsextending outwardly from the inlet of said first ducts, said outwardlyextending flanges and said extending portions from an inlet conduitconnected with the inlet of each of said first ducts;

a second flange is formed on the end of said inlet conduit;

plate members are bonded to the edges of the second flange and bonded tosaid buffer fluid enclosure and to both exterior plates to form a hollowannular compartment around said inlet ducts; and

means are provided to allow the buffer fluid to flow between said hollowannular compartment and said enclosure.

4. The heat exchanger of claim 2 wherein:

said contoured plate walls are further shaped so that, when they aredisposed face-to-face, each of said third ducts is U-shaped;

two pipes extend through the buffer fluid enclosure and connect with therespective legs of said third ducts so that said second fluid flowsintoone leg of each of the U- shaped third ducts and flows out of the otherleg thereof; and

means are operably associated with said buffer fluid enclosure tomaintain said buffer fluid at a higher pressure than the pressure ofboth said first and said second fluids.

5. The heat exchanger of claim 3 wherein:

said plate walls are further shaped so that when they are disposedface-to-face each of said third ducts is U-shaped; and

said manifold means includes two pipes extending through said bufferfluid enclosure and connect with each of said third ducts so that saidsecond fluid flows into one leg of each of the U-shaped third ducts andout of the other leg thereof.

6. The heat exchanger of claim 5 wherein a pressure relief .valve isoperably associated with said enclosure for the buffer 7. Theexchangerof claim 1 wherein:

a first passageway communicates with said first ducts;

said first passageway is formed by an inner wall surrounded by an outerwall forming a hollow annular compartment; and

means are provided to allow the buffer fluid to flow between the hollowannular compartment and said enclosure.

8. A heat exchanger comprising: an enclosure for containing a bufferfluid;

a plurality of spaced parallel plates disposed within said enclosure;

a plurality of first spacer elements arranged between alternately spacedparallel plates to define a plurality of first passageways within saidenclosure to convey a first fluid;

a plurality of second spacer elements arranged between the alternatelyspaced parallel plates not including said first spacer elements todefine a plurality of second passageways communicating with the bufferfluid within said enclosure;

a plurality of third passageways to convey a second fluid, one of saidthird passageways disposed within each of said plurality of secondpassageways; and

means to maintain said buffer fluid within said enclosure at a pressurehigher than the individual pressure of either the first or second fluid.

9. The heat exchanger of claim 8 wherein said buffer fluid is a liquid.

